Such optical system is, for example, a fluorescence correlation spectroscope or a laser-scanning microscope. In a laser-scanning microscope, there is often the problem that, due to the longitudinal chromatic aberration characteristic of the optical unit (the objective), excitation undesirably occurs at different depths in a sample.
It is known from DE 102 17 544 A1 to construct a collimator using at least two lenses of different optical materials, which collimator serves to reduce the longitudinal chromatic aberration of the objective. However, since the collimator is constructed using at least two lenses of different optical materials, its production is complex and costly.
In view thereof, it is an object of the invention to provide an optical system comprising an optical unit and a collimator, said system allowing the above-described disadvantages to be overcome.